1. Field of the Invention
The present invention relates to a boiling refrigerant-type cooling system. More particularly, the invention relates to a cooling system designed to cool an electric apparatus such as a semiconductor stack by dipping the electric apparatus into a boiling refrigerant enclosed in an airtight container. The circulation of the refrigerant which is accompanied by a vapor-liquid phase change cools the refrigerant.
Description of the Related Art
Boiling refrigerant-type cooling systems as shown in FIGS. 7 and 8 are known in the art. In FIG. 7, an electric apparatus 6 such as a semiconductor stack, which is likely to become a heat source, is completely dipped in a boiling refrigerant 7 that is stored in the boiling refrigerant section 1 of the airtight container 18. The electric apparatus 6 is held so that it may remain in the boiling refrigerant section 1. The leads of the electric apparatus 6 are led out through airtight terminals 5 which adjoin the boiling refrigerant section 1 of the airtight container 18. Above the boiling refrigerant section 1 of the airtight container are installed condensing refrigerant chambers 8 equipped with heat exchanger fins 15. When the refrigerant 7 absorbs the heat loss of the electric apparatus 6, it boils and enters the vapor phase. The vaporized refrigerant then flows into a condensing refrigerant section 2 of the airtight container 18 where it passes around the heat exchanger fins 15, and into an air reservoir 10 located above the condensing refrigerant chambers 8. The outer walls of the condensing refrigerant chambers 8 are so arranged as to adjoin the cooling chambers 9 which contact the vaporized refrigerant. The cooling chambers 9, containing heat exchanger fins 13, are provided with openings on both sides thereof for allowing the outside air to flow therethrough. An electrically insulating material such as freon 113 is used as the boiling refrigerant because high voltage is applied to the electric apparatus inside the boiling refrigerant section 1.
In the boiling refrigerant cooling system constructed as described above, the loss heat from the electric apparatus is released in the outside air when the apparatus is cooled by the boiling refrigerant 7 which circulates in the airtight container. When heat transfers from the electric apparatus 6 to the refrigerant 7, boiling of the refrigerant 7 occurs where the loss heat of the electric apparatus radiates from the electric apparatus. Heat transfer from the vaporized refrigerant occurs with condensation of the vapor in the condensing refrigerant chambers 8 and with convection from the vaporized refrigerant to the heat exchanger fins 13 of the cooling chambers 9. Cooling systems employing a phase changing refrigerant must be made airtight to secure the cooling capacity of the system over a long period of time. The airtightness of the cooling system is normally kept at 10.sup.-7 atm. cc/sec or lower in terms of a leakage, provided that parts of the airtight container are welded or soldered.
In order to maintain the aforementioned airtightness, an upper header 4 and a lower header 3 are respectively welded to the body 2a of the condensing refrigerant section 2 and then the combination is welded to the boiling refrigerant section 1. The airtight terminals 5 for leading the leads of the electric apparatus 6 into the boiling refrigerant section 1 are then arranged with and welded to the boiling refrigerant section 1. The air reservoir 10 formed inside the upper header 4 of the condensing refrigerant section 2 communicates with each of the groove-shaped condensing refrigerant chambers 8 which are divided by the cooling chambers 9. The pressure within the airtight container 18 is thus made uniform to prevent a reduction in the condensing capacity of the condensing refrigerant section 2 due to a trace of air unavoidably penetrating into the airtight container during the use of the cooling system for a long period of time.
The condensing refrigerant chambers 8 and the cooling chambers 9 within the condensing refrigerant section 2 are arranged as shown in FIG. 8. The cooling chambers 9 have groove-like shaped surfaces and a heat exchanger fin 13 for passing the air internally and horizontally. The chambers 9 open to the outside air on both sides of the condensing refrigerant section 2. The condensing refrigerant chambers 8 also have a groove-like surface and a heat exchanger fin 15 which form a passage for passing vaporized refrigerant internally and vertically. The chambers 8 and 9 are alternately partitioned with partition boards 11. In addition, closing members 12 and 14 are used to close the upper and lower sides of the cooling chambers 9 and the front and rear sides of the condensing refrigerant chambers 8 to restrict each chamber to single direction flow.
The heat exchanger fins 13 and 15, the partition boards 11 and the closing members 12 and 14 are made of aluminum to decrease the weight of the cooling system as a whole and to improve the heat exchanging characteristics of the condensing refrigerant chambers 8 and the cooling chambers 9. In order to improve product quality control further, the partition boards 11 may be prepared from brazing material, i.e., aluminum core material claded with brazing filler metals, and then used to construct the condensing refrigerant chambers 8 and the cooling chambers 9. The combination thus constructed is heated and cooled in a salt bath or furnace under predetermined conditions to braze the junctions of the aforementioned members at one time.
Although the condensing refrigerant chambers 8 and the cooling chambers 9 in the airtight container of the boiling refrigerant cooling system thus constructed are brazed at one time, the remaining parts of the airtight container are joined by normal welding processes. The formation of the boiling refrigerant section 1, the joining of the body 2a and the headers 3 and 4 in the condensing refrigerant section 2, and the joining of the boiling refrigerant section 1 and the condensing refrigerant section 2 are all completed with a normal welding process. Accordingly, the manual welding operations, which require a significant skilled labor input, reduce airtightness reliability because of welding distortion and bubbles or because of foreign matter penetration into the airtight container. As a result, the benefit of simultaneous member-brazing will be largely lost and economy will be reduced, particularly when similar products are mass-produced.
Extreme high airtightness is required for the airtight container of a boiling refrigerant cooling system to prevent boiling refrigerant leakage and outside air penetration. Additionally, it is essential to prevent noxious foreign matter from mixing with the charged body of the electrical apparatus. Finally, effective quality control and low production cost are desirous, particularly when the boiling refrigerant-type systems are mass-produced.
In view of the shortcomings inherent in conventional boiling refrigerant type cooling systems as described above, it is an object of the present invention to provide a boiling refrigerant-type cooling system wherein all members are prepared from a material coated with solder and formed into desired shapes and the members are joined airtightly and simultaneously under stable conditions to construct an airtight container for a boiling refrigerant-type cooling system. It is a further object of the present invention to produce a cooling system that may be mass-produced under high quality control conditions to produce a highly reliable system with reduced labor, and thus production costs.